I agree with what you are saying entirely. An absolute lack of laws would cause some (not all) people in a society to act in violent ways if there are no organized police squads formed without government aid. In addition, you make a strong point that there would be a lack of a strong military in an anarchist society, leaving it open to invasions and takeovers by other states. Without taxes, the quality of public services would decrease as well. Finally, most people want to live, structured, orderly, safe lives, which a government can provide.

It is necessary for a nation to have a government for several reasons. First, governments have the power to regulate and fund public works, including bridges, roads, and hospital. Without regulations in place for these things, they could become much more dangerous to utilize, and there would be no way to fund them in the first place. Second, without a government, violent criminals would be more difficult to deal with, as there would be no police to enact justice. Granted, most people aren't bloodthirsty criminals, but how would one punish, say, a murderer in a police-less society? (Vigilant police squads might also form, but they would cause more harm than good.) Third, governments provide financial aid to lower-income citizens through systems such as food stamps. The amount of people in poverty in a given nation would grow exponentially. Fourth, if a society's government were to fall, the society would just create a new government themselves. A society must be organized in some way in order to function and prosper.